Global carbon emissions from urban lakes

Abstract

Lakes are significant emitters of carbon into the atmosphere despite representing a small portion of continental land cover. However, the impact of urban lakes on global carbon emissions needs to be better understood due to increasing human population and the constant warming of the earth's surface. Our objective was to determine the global contribution of urban lakes to carbon emissions and identify the factors controlling these emissions. We estimated the area of urban lakes globally using GIS while CO2 and CH4 emissions were found from literature review . We found that urban lakes covered about 17,458 km² and emits 72.5 Tg CO2 equivalent annually, which is five times higher than the emissions from global reservoirs, in proportion to the land cover area occupied by them. This emission is equivalent to 2.8x109 cars traveling 96,000 km, or twice the Pan-American Highway, which is the longest highway in the world. Urban lakes were mainly carbon sources to the atmosphere (82%), however, a small part was absorbed (18%). The annual global increase in urban lake land cover is approximately 102.5 km², increasing 0.71 Tg CO2 equivalent emissions annually. The GHG emissions were positively driven by temperature and a set of other variables. Eutrophication showed a disproportionately higher impact on emissions, being 900 times higher in eutrophic lakes than in non-eutrophic ones. Carbon emissions was positively correlated with TP and TOC and increased latitudinally towards the equator, with higher values in the tropical zone (36.2 ± 62.1g CO2 eq m-² d-1 ) and lower values in the continental zone (2.62 ± 2.0 g CO2 eq m- ² d1 ). The surface area of the system and carbon emissions had a quadratic relationship, increasing to a certain size (>0.1 to 1 km²) from which the value tended to decrease, probably due to a dilution effect of the components that promote GHG production and emission in the systems. According to PLS analysis, human population density, road density, and gross domestic product explained CH4 emissions variations. We assume that urban lakes' carbon emissions are anthropogenic, and their output is expected to increase due to the enlarging of urban lake areas, eutrophication effect and warming of the Earth's surface. Our findings provide strong evidence for decision makers and governments to implement initiatives toward water quality and de-eutrophication measures to protect the global climate from such anthropogenic impacts. By doing so, we can both decrease carbon emissions from urban lakes and still benefit from the services they provide.